Corticotropin-releasing factor depolarizes rat lateral vestibular nuclear neurons through activation of CRF receptors 1 and 2.

Corticotropin-releasing factor (CRF) is a neuropeptide mainly synthesized in the hypothalamic paraventricular nucleus and has been traditionally implicated in stress and anxiety. Intriguingly, genetic or pharmacological manipulation of CRF receptors affects locomotor activity as well as motor coordination and balance in rodents, suggesting an active involvement of the central CRFergic system in motor control. Yet little is known about the exact role of CRF in central motor structures and the underlying mechanisms. Therefore, in the present study, we focused on the effect of CRF on the lateral vestibular nucleus (LVN) in the brainstem vestibular nuclear complex, an important center directly contributing to adjustment of muscle tone for both postural maintenance and the alternative change from the extensor to the flexor phase during locomotion. The results show that CRF depolarizes and increases the firing rate of neurons in the LVN. Tetrodotoxin does not block the CRF-induced depolarization and inward current on LVN neurons, suggesting a direct postsynaptic action of the neuropeptide. The CRF-induced depolarization on LVN neurons was partly blocked by antalarmin or antisauvagine-30, selective antagonists for CRF receptors 1 (CRFR1) and 2 (CRFR2), respectively. Furthermore, combined application of antalarmin and antisauvagine-30 totally abolished the CRF-induced depolarization. Immunofluorescence results show that CRFR1 and CRFR2 are co-localized in the rat LVN. These results demonstrate that CRF excites the LVN neurons by co-activation of both CRFR1 and CRFR2, suggesting that via the direct modulation on the LVN, the central CRFergic system may actively participate in the central vestibular-mediated postural and motor control.

Cortico-reticulo-spinal circuit reorganization enables functional recovery after severe spinal cord contusion.

Severe spinal cord contusions interrupt nearly all brain projections to lumbar circuits producing leg movement. Failure of these projections to reorganize leads to permanent paralysis. Here we modeled these injuries in rodents. A severe contusion abolished all motor cortex projections below injury. However, the motor cortex immediately regained adaptive control over the paralyzed legs during electrochemical neuromodulation of lumbar circuits. Glutamatergic reticulospinal neurons with residual projections below the injury relayed the cortical command downstream. Gravity-assisted rehabilitation enabled by the neuromodulation therapy reinforced these reticulospinal projections, rerouting cortical information through this pathway. This circuit reorganization mediated a motor cortex-dependent recovery of natural walking and swimming without requiring neuromodulation. Cortico-reticulo-spinal circuit reorganization may also improve recovery in humans.

Oestradiol effects on neuroendocrine responses induced by water deprivation in rats.

Water deprivation (WD) induces changes in plasma volume and osmolality, which in turn activate several responses, including thirst, the activation of the renin-angiotensin system (RAS) and vasopressin (AVP) and oxytocin (OT) secretion. These systems seem to be influenced by oestradiol, as evidenced by the expression of its receptor in brain areas that control fluid balance. Thus, we investigated the effects of oestradiol treatment on behavioural and neuroendocrine changes of ovariectomized rats in response to WD. We observed that in response to WD, oestradiol treatment attenuated water intake, plasma osmolality and haematocrit but did not change urinary volume or osmolality. Moreover, oestradiol potentiated WD-induced AVP secretion, but did not alter the plasma OT or angiotensin II (Ang II) concentrations. Immunohistochemical data showed that oestradiol potentiated vasopressinergic neuronal activation in the lateral magnocellular PVN (PaLM) and supraoptic (SON) nuclei but did not induce further changes in Fos expression in the median preoptic nucleus (MnPO) or subfornical organ (SFO) or in oxytocinergic neuronal activation in the SON and PVN of WD rats. Regarding mRNA expression, oestradiol increased OT mRNA expression in the SON and PVN under basal conditions and after WD, but did not induce additional changes in the mRNA expression for AVP in the SON or PVN. It also did not affect the mRNA expression of RAS components in the PVN. In conclusion, our results show that oestradiol acts mainly on the vasopressinergic system in response to WD, potentiating vasopressinergic neuronal activation and AVP secretion without altering AVP mRNA expression.

Protective effects of hypothalamic proline-rich peptide and cobra venom Naja Naja Oxiana on dynamics of vestibular compensation following unilateral labyrinthectomy.

We tested the action of proline-rich peptide (PRP-1) and cobra venom Naja Naja Oxiana (NOX) on Deiters' nucleus neurons at 3rd, 15th and 35th days after unilateral labyrinthectomy (UL). Early and late tetanic, post-tetanic potentiation and depression of Deiters'neurons to bilateral high frequency stimulation of hypothalamic supraoptic and paraventricualar nuclei was studied. The analysis of spike activity was carried out by mean of on-line selection and special program. The complex averaged peri-event time and frequency histograms shows the increase of inhibitory and excitatory reactions of Deiters' neurons at early stage of vestibular compensation following PRP-1 and NOX injection, reaching the norm at the end of tests. In histochemical study the changes in Ca(2+)-dependent acidic phosphatase (AP) activity in neurons was discovered. It was shown that in UL animals the total disappearance or delay of decolorizing of Deiters' neurons lead to neurodegenerative pattern as cellular "shade". AP activity after UL and PRP-1 injection exerts more effective recovery of neurons in comparison with events, observed after the administration of NOX. The data of this study indicate that PRP-1 and NOX are protectors, which may successfully recover the disturbed vestibular functions.

Type B GABA receptors contribute to the restoration of balance during vestibular compensation in mice.

Following unilateral vestibular damage (UVD), vestibular compensation restores both static and dynamic vestibular reflexes. The cerebellar cortex provides powerful GABAergic inhibitory input to the vestibular nuclei which is necessary for compensation. Metabotropic GABA type B (GABA(B)) receptors in the vestibular nuclei are thought to be involved. However, the contribution of GABA(B) receptors may differ between static and dynamic compensation. We tested static and dynamic postural reflexes and gait in young mice, while they compensated for UVD caused by injection of air into the vestibular labyrinth. The effects of an agonist (baclofen), an antagonist (CGP56433A) and a positive allosteric modulator (CGP7930) of the GABA(B) receptor were evaluated during compensation. Static postural reflexes recovered very rapidly in our model, and baclofen slightly accelerated recovery. However, CGP56433A significantly impaired static compensation. Dynamic reflexes were evaluated by balance-beam performance and by gait; both showed significant decrements following UVD and performance improved over the next 2 days. Both CGP56433A and baclofen temporarily impaired the ability to walk on a balance beam after UVD. Two days later, there were no longer any significant effects of drug treatments on balance-beam performance. Baclofen slightly accelerated the recovery of stride length on a flat surface, but CGP7930 worsened the gait impairment following UVD. Using immunohistochemistry, we confirmed that GABA(B) receptors are abundantly expressed on the vestibulospinal neurons of Deiters in mice. Our results suggest that GABA(B) receptors contribute to the compensation of static vestibular reflexes following unilateral peripheral damage. We also conclude that impairment of the first stage of compensation, static recovery, does not necessarily result in an impairment of dynamic recovery in the long term.

[Effects of various neuromediators and regulatory peptides on the impulse activity of neurons in the lateral vestibular nucleus].

The myoelectrode technique and microiontophoresis of physiologically active substances were applied to cats immobilized with neuromuscular relaxant to show that the classic neuromediators (acetylcholine, norepinephrine, GABA etc.) and regulatory peptides (enkephalins, TRHs, vasoactive intestinal peptide (VIP), somatostatin (SS) and others) can influence directly most neurons (58 to 100%) in the lateral vestibular nucleus (LVN). Enkephalins, VIP and SS retained largely their inhibitory effect on the neuron impulse activity in the presence of L-glutamate. Also, enkephalins, VIP and SS are able to stimulate or suppress the inhibitory effect of GABA and glycine. Consequently, the substances under study may act as LVN neuromediators and/or neuromodulators.

Static and dynamic membrane properties of lateral vestibular nucleus neurons in guinea pig brain stem slices.

In vitro intracellular recordings of central vestibular neurons have been restricted so far to the medial vestibular nucleus (MVN). We performed intracellular recordings of large Deiters' neurons in the lateral vestibular nucleus (LVN) to determine their static and dynamic membrane properties, and compare them with those of type A and type B neurons identified in the MVN. Unlike MVN neurons (MVNn), the giant-size LVN neurons (LVNn) form a homogeneous population of cells characterized by sharp spikes, a low-amplitude, biphasic after-hyperpolarization like type B MVNn, but also an A-like rectification like type A MVNn. In accordance with their lower membrane resistance, the sensitivity of LVNn to current injection was lower than that of MVNn over a large range of frequencies. The main difference between LVNn and MVNn was that the Bode plots showing the sensitivity of LVNn as a function of stimulation frequency were flatter than those of MVNn, and displayed a weaker resonance. Furthermore, most LVNn did not show a gradual decrease of their firing rate modulation in the frequency range where it was observed in MVNn. LVNn synchronized their firing with the depolarizing phase of high-frequency sinusoidal current injections. In vivo studies have shown that the MVN would be mainly involved in gaze control, whereas the giant LVNn that project to the spinal cord are involved in the control of posture. We suggest that the difference in the membrane properties of LVNn and MVNn may reflect their specific physiological roles.

Spontaneous activity in rat vestibular nuclei in brain slices and effects of acetylcholine agonists and antagonists.

Extracellular recording was used to investigate spontaneously active neurons in all four major nuclei of the rat vestibular nuclear complex (VNC) in brainstem slices. The density of spontaneously active neurons was highest in the medial vestibular nucleus (MVN), slightly lower in the superior (SuVN) and spinal (SpVN) nuclei, and lowest in the lateral vestibular nucleus (LVN). We compared the effects of acetylcholine agonists and antagonists on spontaneously discharging neurons in MVN, SuVN, and SpVN with those in the nearby dorsal cochlear nucleus (DCN). The proportion of neurons responding to carbachol was greatest in DCN and smallest in SpVN. Unlike in DCN, some neurons in MVN, SuVN, and SpVN showed decreased firing during carbachol or muscarine. Magnitudes of responses to carbachol and muscarine were closely correlated (P<0.01). MVN neurons possessed nicotinic as well as muscarinic receptors. Activation of either type was unaffected by blocking synaptic transmission. The IC(50) values for the muscarinic subtype-preferential antagonists were compared, and tropicamide, preferential for M(4), was the most potent. Our results suggest that: (1) the relative numbers of spontaneously active neurons in rat VNC differ among nuclei; (2) acetylcholine agonists elicit changes in mean firing rates of neurons in MVN, SuVN and SpVN, but fewer neurons respond, and responses are smaller than in DCN; (3) both muscarinic and nicotinic acetylcholine receptors are present on MVN neurons, but muscarinic receptors may be more prominent.

Modulation by acute stress of chloride permeation across microdissected vestibular neurons membranes: different results in two rabbit strains and CRF involvement.

Free hand isolation of adult rabbit vestibular Deiters' neurons and dissection of their single membranes allows the study of their ionic permeability characteristics in a microchambers device. In the case of hare-like rabbits, the dissection of such membranes presents evidence of a high basal permeation of labelled chloride, possibly related to mechanical disturbance of the plasma membrane-related cytoskeleton and activation of chloride channels. This did not apply to the laboratory strain of white New Zealand rabbits. However, membranes from hare-like rabbits which were stressed by being rotated on a platform before the experiment, behaved like those from the New Zealand strain. Vice versa, habituation to handling day after day of New Zealand rabbits resulted in a chloride permeation equal to that of unstressed hare-like rabbits. We propose that the stressful conditions result in the release of neurochemical messages to the vestibular Deiters' cells which influence their electrophysiological behavior. The corticotropin releasing factor (CRF), a stress-related peptide present in the climbing fibers, actually blocks the basal chloride permeation across the Deiters' membranes and this effect is partially reversed by its receptor antagonist, alpha-helical CRF [9-41].

Effects of intra-vestibular nucleus injection of the group I metabotropic glutamate receptor antagonist AIDA on vestibular compensation in guinea pigs.

Removal of the peripheral vestibular receptor cells in one inner ear (unilateral vestibular deafferentation, UVD) results in a syndrome of ocular motor and postural disorders, many of which disappear over time in a process of behavioural recovery known as vestibular compensation. Excitatory amino acid receptors, in particular the N-methyl-D-aspartate (NMDA) receptor, have been implicated in vestibular compensation; however, the metabotropic glutamate receptors (mGluRs) have not been studied in this context. The aim of this study was to determine whether group I mGluRs in the brainstem vestibular nucleus complex (VNC) ipsilateral to the UVD are involved in vestibular compensation of the static symptoms of UVD in guinea pig. The selective group I mGluR antagonist (RS)-1-aminoindan-1,5,dicarboxylic acid (AIDA) was continuously infused into the ipsilateral VNC for 30-min pre-UVD and 30-min post-UVD by cannula, at a rate of 1 microl/h, using one of four doses: 0.1 fg, 0.1 pg, 0.1 ng or 0.1 microg (n=5 animals in each case). In control conditions, a 0.1-fg (n=4) or 0.1-microg (n=5) NaOH vehicle was infused into the ipsilateral VNC using the same protocol. In order to control for the possibility that AIDA disrupted spontaneous neuronal activity in the VNC in normal animals, 0.1 microg AIDA (n=4) or 0.1 microg NaOH (n=2) was infused into the VNC in labyrinthine-intact animals. In both groups, static symptoms of UVD (i.e. spontaneous nystagmus, SN, yaw head tilt, YHT and roll head tilt, RHT) were measured at 8, 10, 12, 15, 20, 25, 30, 35, 45 and 50 h post-UVD. In addition, the righting reflex latency (RRL) was measured in labyrinthine-intact animals in order to assess whether AIDA impaired motor coordination in labyrinthine-intact animals. In UVD animals, the highest dose of AIDA significantly reduced SN frequency and changed its rate of compensation (P<0.001 and P<0.0001, respectively). This dose of AIDA also caused a significant reduction in YHT (P<0.005) as well as a significant change in its rate of compensation (P<0.0001). However, RHT was not significantly affected. In the labyrinthine-intact animals, AIDA infusion did not induce a UVD syndrome, nor did it significantly affect RRL. These results suggest that group I mGluRs in the ipsilateral VNC may be involved in the expression of ocular motor and some postural symptoms following UVD. Furthermore, group I mGluRs may not contribute to the resting activity of vestibular nucleus neurons.

Stimulation of chloride in-->out permeation across the Deiters' neuron membrane by pentobarbital on the cytoplasmic side: additional evidence of GABA(A) receptors acting as chloride extrusion pumps.

Pentobarbital stimulates 36Cl- permeation across single Deiters' membranes in a microchamber system, acting on classical, extracellularly facing, GABA(A) receptors. However, when applied on the membrane cytoplasmic side it activates per se labeled chloride in-->out permeation. No effect was found on chloride out-->in permeation. Similarly, at lower concentrations it facilitates the increase of 36Cl- in-->out permeation by application of GABA on the membrane inside, again via asymmetric chloride channels allowing in-->out but not out-->in passage. These data confirm that on the Deiters' membrane cytoplasmic side there are structures behaving pharmacologically as GABA(A) receptors whose function is that of a Cl- extrusion pump. This mechanism involves a cycle of activation-phosphorylation/desensitization-reactivation of the receptor complexes.

P2X receptors in cochlear Deiters' cells.

1. The ionotropic purinoceptors in isolated Deiters' cells of guinea-pig cochlea were characterized by use of the whole-cell variant of the patch-clamp technique. 2. Extracellular application of adenosine 5'-triphosphate (ATP) induced a dose-dependent inward current when the cells were voltage-clamped at -80 mV. The ATP-induced current showed desensitization and had a reversal potential around -4 mV. 3. Increasing intracellular free Ca2+ by decreasing the concentration of EGTA in the pipette solution reduced the amplitude of the ATP-gated current. 4. The order of agonist potency was: 2-methylthioATP (2-meSATP)>ATP>benzoylbenzoyl-ATP (BzATP)>alpha,beta-methyleneATP (alpha,beta,meATP>adenosine 5'-diphosphate (ADP)>uridine 5'-triphosphate (UTP)>adenosine 5'-monophosphate (AMP)=adenosine (Ad). 5. Pretreatment with forskolin (10 microM), 8-bromoadenosine-3',5'-cyclophosphate (8-Br-cyclic AMP, 1 mM), 3-isobutyl-1-methylxanthine (IBMX, 1 mM) or phorbol-12-myristate-13-acetate (PMA, 1 microM) reversibly reduced the ATP-induced peak current. 6. The results are consistent with molecular biological data which indicate that P2X2 purinoceptors are present in Deiters' cells. In addition, the reduction of the ATP-gated current by activators of protein kinase A and protein kinase C indicates that these P2X2 purinoceptors can be functionally modulated by receptor phosphorylation.

Additional pharmacological evidence that endogenous ATP modulates cochlear mechanics.

In the cochlea, outer hair cells (OHCs) generate the active cochlear mechanics whereas the supporting cells, such as Deiters' cells and Hensen's cells, may play a role in both the active and passive cochlear mechanics. The presence of receptors for adenosine triphosphate (ATP) on OHCs, Deiters' cells and Hensen's cells indicates that endogenous ATP may have a role in cochlear mechanics. To explore this possibility, the effects of the ATP antagonist, pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), were studied in guinea pig both in vitro on isolated OHCs, Deiters' cells, Hensen's cells and pillar cells using the whole-cell configuration of the patch-clamp technique, and in vivo on sound evoked cochlear potentials (cochlear microphonic, CM; summating potential, SP; compound action potential, CAP) and distortion product otoacoustic emissions (DPOAEs) using cochlear perilymphatic perfusion. Results show that PPADS (100 microM) reduced the inward current evoked by 5-10 microM ATP in OHCs, Deiters' cells, Hensen's cells and pillar cells. This effect of PPADS was slow in onset and was slowly reversed to a varying degree in the different cell types. In vivo application of PPADS in increasing concentrations reduced the sound evoked CAP, SP and increased N1 latency starting at about 0.33 mM (SP) and 1 mM (CAP and N1 latency). PPADS (0.33-1 mM) reversibly suppressed the initial value of the quadratic DPOAE and reversed the 'slow decline' in the quadratic DPOAE that occurs during continuous stimulation with moderate level primaries. These results, together with the similar effects of the ATP antagonist suramin reported previously (Skellett et al., 1997), may be evidence that endogenous ATP acting on cells in the organ of Corti alters cochlear mechanics.

Receptor-targeted delivery of an intracellular toxin to outer hair cells by fibroblast growth factor.

The presence and distribution of functional, high-affinity receptors for fibroblast growth factors (FGFs) in the neonatal organ of Corti were probed using the intracellular toxin saporin conjugated to basic FGF (FGF-2). FGFs that bind to high-affinity FGF receptors are internalized as part of the normal process of receptor inactivation. The receptor can thus be used for the targeted delivery of molecules conjugated to FGF into the cytoplasm. Incubation of postnatal day 5 (P5) rat organ of Corti cultures with FGF-saporin caused a dose dependent destruction of outer hair cells, Deiters cells and outer pillar cells. Inner hair cells and other cells were unaffected. Organ of Corti cultures at P0 and P10 showed much less damage than at P5. The results suggest that outer hair cells and adjacent supporting cells in the organ of Corti transiently express high-affinity FGF receptors, and that these receptors can mediate the intracellular delivery of bioactive molecules.

Pharmacological evidence that endogenous ATP modulates cochlear mechanics.

In the cochlea, outer hair cells (OHCs) and Deiters' cells most likely contribute to the generation of active cochlear mechanics. The presence of ATP receptors on these cells indicates that endogenous ATP may have a role in cochlear mechanics. To explore this possibility, the effects of ATP antagonists were studied both in vivo on distortion product otoacoustic emissions (DPOAEs) using cochlear perfusion and in vitro on isolated OHCs and Deiters' cells using the whole-cell configuration of the patch-clamp technique. Results show that extracellular application of 5-10 microM ATP to OHCs and Deiters' cells induced an inward current that was reduced by both suramin (100 microM) and cibacron (100 microM). Cibacron reduced the voltage gated currents in Deiters' cells and increased them in OHCs, while suramin had no effect. In addition, cibacron induced a hyperpolarizing shift of the half activation voltage of the whole cell currents in Deiters' cells. Suramin (0.1-1 mM) reversibly suppressed the 'slow decline' in the quadratic DPOAE that occurs during continuous stimulation with moderate level primaries. This effect of suramin may be evidence that endogenous ATP alters active cochlear mechanics.

Differences in the distribution of responses to ATP and acetylcholine between outer hair cells of rat and guinea pig.

Adenosine 5' triphosphate (ATP) and acetylcholine (ACh) are neurotransmitters (ACh) and/or modulators (ATP) in the mammalian cochlea. In guinea pig, it appears that both neurotransmitters have a similar response distribution, with larger responses being evoked by the ligands in short hair cells compared to long hair cells (e.g., Chen et al., 1995b. Noise exposure alters the response of outer hair cells to ATP. Hear. Res. 88, 215-221.; Erostegui et al., 1994. In vitro pharmacologic characterization of a cholinergic receptor on outer hair cells. Hear. Res. 74, 135 147). The purpose of the present study was to test whether the distribution of responses to ACh and ATP in the OHCs of rat is the same as guinea pig. The ligand-induced current was monitored using the whole-cell configuration of the patch-clamp technique. Results show that in guinea pig OHCs, extracellular application of 100 microM ATP induced a current response in a majority of the same cells that responded to the application of 100 microM ACh. In contrast in rat OHCs, 100 microM ATP did not induce a current in the majority of cells that responded to the application of 100 microM ACh. N-methyl-glucamine (NMG+) substituted for K+ in the pipette solution failed to unmask an ATP-evoked inward current in rat OHCs. In addition, no response was produced in rat or guinea pig OHCs by adenosine, adenosine 5'-monophosphate (AMP) or adenosine 5'-diphosphate (ADP) at 100 microM. Results suggest that in guinea pig ACh-gated channels are present on most of the same OHCs that have ATP-gated ion channels, whereas in rat ACh-gated ion channels are present without ATP-gated channels on some OHCs.

Modulation by calcium of Deiters' neuron GABAA receptors in the rabbit.

The function of classical GABAA receptors of the rabbit Deiters' neurons has been studied at the single membrane level by a biochemical micromethod involving the study of labelled chloride permeation. In particular, labelled chloride permeation across microdissected fresh single membranes was studied in a microchamber system. The stimulation of 36Cl- out-->in permeation by "extracellular" GABA was determined under different conditions in the respect of Ca++. When the conditions were such that "intracellular" Ca++ was 0.02 microM there appeared to be an optimal effect by GABA on chloride passage. Conditions presumably resulting in an increase of [Ca++]i beyond the level reported above led to a decreased GABA effect, especially at the highest GABA concentrations used (> or = 10(-4)M). However, complete removal of Ca++ by a high (12 mM) intracellular EGTA concentration erased completely the GABA effect. These results indicate that in these neurons an optimal GABAA receptor function requires [Ca++]i levels well below micromolar. The high [EGTA]i effect seems to imply that too low a [Ca++]i is also harmful to the proper function of these GABAA receptors. However, an alternative explanation is possible.

Co-administration of the neurotrophic ACTH(4-9) analogue, ORG 2766, may reduce the cochleotoxic effects of cisplatin.

In this study the effect of the neurotrophic ACTH(4-9) analogue, ORG 2766, on cisplatin cochleotoxicity was investigated with both light- and transmission electron microscopy. Guinea pigs were treated with either cisplatin+ORG 2766 (n = 11) or cisplatin + physiological saline (n = 9). All animals treated with cisplatin + physiological saline showed complete loss of outer hair cells (OHC) and degeneration of the organ of Corti in the basal cochlear turns, while partial OHC loss was found in the middle and apical turns. The inner hair cells (IHC) and other cochlear tissues were not affected. Eight animals from the group treated with cisplatin + ORG 2766 demonstrated similar pathological changes, but to a lesser degree, especially in the middle turns. The three remaining animals demonstrated no cochlear alterations at all, light-microscopically, and only minor subcellular changes in the OHCs at the ultrastructural level. Electrophysiologically, these three animals showed normals compound action potential (CAP) amplitudes at stimulus frequencies from 0.5 to 16 kHz and normal cochlear microphonics (CM) in the frequency range from 0.5 to 8 kHz. The other animals treated with cisplatin + ORG 2766 showed a severe loss in their CAPs and CM, except for one showing intermediate loss. All animals from the group treated with cisplatin alone showed a severe loss in their CAPs and CM. Endolymphatic hydrops was present in all animals from the cisplatin- and the cisplatin + ORG 2766-treated groups. These data indicate that daily, concomitant administration of ORG 2766 may reduce OHC loss and subsequent degeneration of the organ of Corti in cisplatin-treated guinea pig cochleas.

Does long-term potentiation occur in guinea-pig Deiters' nucleus?

Long-term potentiation (LTP) was studied in the lateral vestibular nucleus (LVN-Deiters' nucleus) in guinea-pigs in vivo. Field potentials and extracellular single unit discharges were recorded in the LVN following electrical stimulation of the ipsilateral VIIIth nerve. High-frequency stimulation (HFS) of the VIIIth nerve fibres produced LTP of the monosynaptic component of the vestibular field potential. The LTP of the field potentials was paralleled by an increase of the evoked spike activity. Intranuclear administration of the NMDA antagonist MK-801 prevented LTP of the monosynaptic component of the vestibular field potentials and significantly suppressed the spontaneous firing of lateral vestibular neurones in a dose-dependent fashion. These results demonstrate that synapses between primary afferent fibres and second order LVN neurones undergo long lasting changes following HFS of the ipsilateral vestibular nerve.

Somatotopical effects of local microinjection of GABAergic agents in Deiters nucleus on the posturokinetic responses to cortical stimulation.

The postural adjustments that accompany the limb flexion following stimulation of the motor cortex in the cat are in part at least mediated by the lateral vestibular nucleus (LVN). In fact, inactivation of vestibulospinal (VS) neurons by unilateral injection of GABA agonists into the LVN decreased the early component of the responses in all of the postural limbs without modifying the threshold, latency, or amplitude of the cortically induced flexion movement. Just the opposite result was obtained after injection into the same structure of GABA antagonists. Experiments were performed to find out whether these VS influences were somatotopically organized. Microinjection of 0.25 microL of the GABA-A agonist muscimol or the GABA-B agonist baclofen (at 1.5 to 4 micrograms/microL saline) into the rostroventral part of the LVN (rvLVN) of one side produced hypotonia in the ipsilateral and hypertonia in the contralateral forelimb. The same injection also reduced the early component of the postural responses to cortical stimulation in both forelimbs, but not in the hindlimbs. On the other hand, unilateral injection of the same agents into the dorsocaudal part of the LVN (dcLVN) produced similar effects, but they were limited to the hindlimbs. The results obtained, which lasted for about 2 to 3 h, were not only site-specific but were also dose-dependent. Injection into the rvLVN or dcLVN of 0.25 microL of the GABA-A antagonist bicuculline or the GABA-B antagonist phaclofen (at 8 or 5 micrograms/microL saline) produced localized changes in posture as well as in the post-urokinetic responses to cortical stimulation. These were opposite in sign to those elicited by the corresponding agonists. In conclusion, it appears that: 1) the motor cortex utilizes descending volleys passing through the LVN in order to elicit the early postural adjustments during a cortically induced limb movement; 2) the resulting VS influences are somatotopically organized; 3) the amplitude of these postural responses can be affected by inhibitory influences probably exerted by Purkinje cells of the cerebellar vermis on the related VS neurons through both GABA-A and GABA-B receptors.